1. Field of the Invention
The present invention relates to a technical field of a drive apparatus, a drive method, a program for drive, an Information record medium for drive, and an information processing apparatus for drive. Specifically, the present invention relates to a drive apparatus and a drive method for making a light beam emitting device drive and emit a light beam therefrom, a program for drive used for this drive, an Information record medium in which the program for drive is recorded, and an information processing apparatus including this drive apparatus and being provided for recording or reproducing the information.
2. Related Art
In recent days, when information is recorded into or reproduced from an optical recording medium such as a digital versatile disc (DVD), a laser beam is ordinarily used as a recording and reproducing light beam A element for emitting this laser beam is a semiconductor laser device is frequently used because its cost is low and its size is small.
Because the semiconductor laser device generally emits a laser beam in a so-called single mode, for the purpose such that a noise included in the laser beam is to be reduced, a conventional semiconductor laser device can be driven in a so-called multimode for a conventional record and reproduction of optical information. In this, in order to drive the semiconductor laser device in the multimode, a signal obtained by superposing a superposition signal having a preset frequency on a drive signal for the semiconductor laser device is inputted into the semiconductor laser device.
It is known that when the frequency of the superposition signal varies by a reason such as temperature characteristics, a noise increases as a result of the variation. However, in a conventional red color semiconductor laser used for recording information to and reproducing information from a DVD, even though the noise increases as a result of the variation of the frequency of the superposition signal as designated by a broken line in FIG. 1A (in FIG. 1, referred to as a superposition frequency), the noise remains at a level acceptable for the reproduction of information or less, a reproduction itself is not affected as long as for example the intensity of the laser beam is in the vicinity of what required in the reproduction operation. Accordingly, when the conventional red color laser is used, it is unnecessary to consider a countermeasure to the above mentioned frequency variation of the superposition signal.
Meanwhile, in recent yeas, an optical disk having a memory size higher than the conventional DVD is proposed. For this, a blue-violet semiconductor laser is used as a light source for recording information to and reproducing information from the optical disk. In this blue-violet semiconductor laser, a drive signal obtained by superposing a superposition signal is used to drive in a multimode operation for the purpose of reducing the noise in a similar manner to that in the conventional red color semiconductor laser.
However, according to an experiment conducted by an inventor et al of the present invention, in a case where the above blue-violet semiconductor laser is used as a light source, it is confirmed that the amount of noise generated when the superposition signal varies is more in the blue-violet semiconductor laser than in the conventional red color semiconductor laser as shown in FIG. 1B. Further, it is confirmed that the noise components of the blue-violet semiconductor laser may exceed the noise level acceptable to the reproduction even though the intensity of laser beam is in the vicinity of what necessary for the reproduction of the information as shown in FIG. 1B. Further, it is confirmed that the blue-violet semiconductor laser has output characteristics different from those of the red color semiconductor laser as shown in FIG. 1B.
In this, the above mentioned influences of the noise components of the laser beam derived from the frequency variation of the superposition signal can be relatively reduced by increasing the power of the laser beam However, at a time of reproducing information from a rewritable optical disk, there may be a case where a pit for record may be deformed or vanished by the increased intensity of the light beam for the reproduction and thereby the originally recorded information is erased at the time of reproduction.
Thus there has been a demand for a development which can certainly reduce the noise of the laser beam of the multimode operation in the case of using the blue-violet semiconductor laser.
The present invention is provided to solve the above mentioned problems and to provide a drive apparatus, a drive method, a program for drive, an Information record medium for drive, and an information processing apparatus for drive, all of which can respectively prevent the instability of the frequency of the superposition signal for noise reduction from resulting a noise even in a case where the laser intensity is low.
According to a first aspect of the invention, there is provided a drive apparatus including:
a superposition device which superposes a superposition signal on a drive signal for driving a light beam emission device that emits a light beam and which outputs the drive signal on which the superposition signal is superposed to the light beam emission device,
a reference clock signal generation device which generates a reference clock signal,
a frequency change device which changes a frequency of the superposition signal based on a quality index for indicating a quality of a reproduction signal that is obtained from a reflection light that is the light beam reflected on a record medium,
a phase locked loop device which controls the changed frequency so as to be constant by a feedback method in use of the generated reference clock signal.
According to a second aspect of the invention, there is provided a drive apparatus according to the preceding aspect, further including:
a dividing unit included in the phase locked loop device, wherein
the frequency change device changes the frequency by changing a dividing ratio in the dividing unit.
According to a third aspect of the invention, there is provided a drive apparatus according to the preceding aspect, wherein
the frequency change device changes the frequency in use of the reference clock signal and the dividing ratio of the reference clock signal.
According to a fourth aspect of the invention, there is provided a drive apparatus according to the preceding aspect, further including:
a current change device which changes the current of the superposition signal based on the quality index.
According to a fifth aspect of the invention, there is provided a drive apparatus according to the preceding aspect, further including:
a discrimination device which discriminates whether or not a record medium is a recordable record medium, wherein
the current change device changes the current so that the current for the recordable record medium is smaller than a current for a read only record medium as the record medium.
According to a sixth aspect of the invention, there is provided a drive apparatus according to the preceding aspect, wherein
the quality index is an error rate or a jitter amount in the reproduction signal.
According to a seventh aspect of the invention, there is provided an information processing apparatus including:
the drive apparatus according to the preceding aspect, wherein
the information is subject for at least one of record and reproduction with the emitted light beam.
According to an eighth aspect of the invention, there is provided a drive method including:
a superposition step for superposing a superposition signal on a drive signal for driving a light beam emission device which emits a light beam and for outputting the drive signal on which the superposition signal is superposed to the light beam emission device,
a reference clock signal generation step for generating a reference clock signal,
a frequency change step for changing a frequency of the superposition signal based on a quality index for indicating a quality of a reproduction signal that is obtained from a reflection light that is the light beam reflected on a record medium, and
a control step for controlling the changed frequency so as to be constant by a feedback method using a phase locked loop device.
According to a ninth aspect of the invention, there is provided a drive method according to the preceding aspect further including:
a current change step for changing a current of the superposition signal based on the quality index.
According to a tenth aspect of the invention, there is provided an information medium having a program tangibly demonstrating function comprising steps of:
superposing a superposition signal on a drive signal for driving a light beam emission device that emits a light beam and which outputs the drive signal on which the superposition signal is superposed to the light beam emission device, and
controlling a frequency changed by the computer working as a frequency change device so as to be constant by a feedback in use of the generated reference clock signal, wherein
the computer is driven by the drive program to work as the frequency change device which changes the frequency of the superposition signal based on the quality index indicative of a quality of a reproduction signal obtained from a reflection light that is the light beam reflected on a record medium.
According to an eleventh aspect of the invention, there is provided the information record medium having the program according to the preceding aspects, wherein
the computer is driven to work also as a current change device which changes a current of the superposition signal based on the quality index.